The present invention relates to a disk storage system, a thin film magnetic head therefor and a fabrication method thereof.
The present invention relates to a magnetic core for a magnetic head, and more particularly to a recording head for a dual element head for a disk system having a high recording density.
In recent years, the recording density of a disk storage system has become higher and the magnetic coercive force of recording medium has increased; accordingly, there is a need for a thin film magnetic head which is capable of sufficiently recording on a recording medium having a high magnetic coercive force.
In order to realize this, it is necessary to use a material having a high saturation magnetic flux density (BS) as a core material of the magnetic head. In the past, a 80Nixe2x80x94Fe alloy film of 3 xcexcm thickness has been used for the core material.
However, since the resistivity of the 80Nixe2x80x94Fe alloy film is as low as 16 to 20 xcexcxcexa9xc2x7cm, the eddy current loss becomes large in the high frequency bands. Therefore, the strength of the recording magnetic field of the magnetic head in a high frequency band is decreased, and accordingly the recording frequency is limited to about 30 MHz at maximum.
As an alternative material, Co system amorphous materials and a Fexe2x80x94Alxe2x80x94Si sendust alloy thin film are proposed. However, these materials are not in practical use as yet because the former is thermally unstable, since the material is amorphous, and the latter has a disadvantage in the fabrication process as the magnetic core material for the inductive head, since it requires a high temperature heat treatment at nearly 500xc2x0 C.
In recent years, three-element group materials of Coxe2x80x94Nixe2x80x94Fe have been proposed (Japanese Patent Application Laid-Open No. Sho 60-82,638, Japanese Patent Application Laid-Open No. Sho 61-76,642, Japanese Patent Application Laid-Open No. Sho 64-8,605, Japanese Patent Application Laid-Open No. Hei 2-68,906, Japanese Patent Application Laid-Open No. Hei 2-290,995).
Although the saturation magnetic flux density (BS) of these three-element system materials is as high as 1.5 T, the resistivity is not large and the crystal grain size is not small in the 80Nixe2x80x94Fe alloy; and, in addition to this, there is a disadvantage in the high frequency characteristic as in the 80Nixe2x80x94Fe alloy.
On the other hand, the memory capacity of the disk storage system has been steadily growing year by year, and areal density of a 3.5-inch type disk in production now has been increased up to 350 MB/in2.
In this case, the data recording frequency is nearly 27 MHz, which is near the performance limit of a magnetic head using the 80Nixe2x80x94Fe alloy film or the Coxe2x80x94Nixe2x80x94Fe alloy film.
Although there is proposed in Japanese Patent Application Laid-Open No. 3-68,744 a magnetic film for high frequency use formed by adding Nb, Ta, Cr, Mo to (40-50) Nixe2x80x94Fe through a sputtering method, it is difficult to magnetically form a thick film using a sputtering method because the material has a large magnetocrystalline anisotropy.
One object of the present invention is to provide a disk storage system, a thin film magnetic head therefor and a fabrication method thereof wherein there is provided a disk storage system with a magnetic head for high density recording in a high frequency band.
Another object of the present invention is to provide a magnetic head for high density recording in a high frequency band, that is, a magnetic head which is capable of performing high speed access and has a high transfer rate.
The present invention has been developed for solving the above problems, and involves a thin film magnetic head that is mounted on a disk storage system having a high transfer rate and high recording density, in which there is a magnetic disk rotated above 4000 rpm when the disk storage system is recording or reproducing, and in which the recording frequency is not higher than 45 MHz.
It is required that the magnetic core of the write head be made of a material having a large saturation magnetic flux density (BS) a small magnetic coercive force in the hard axis direction and a large resistivity.
In other words, the range of composition obtainable for a large resistivity and high saturation magnetic flux density is a range containing Ni of 38 to 60 wt % for Nixe2x80x94Fe alloy.
However, when a magnetic film having a thickness of above 2 xcexcm is usually applied to a thin film magnetic head or the like fabricated through a sputtering method, the crystal grain size of the film becomes large, the magnetic coercive force in the hard axis direction is large and the uniaxial magnetic anisotropy is hardly induced, since this composition region is in a range where magnetocrystalline anisotropy is largest.
Therefore, a plating method has been employed in order to suppress the crystal grain size to a small value, and it has been proposed to add a third element, such as Co, Mn, Cr, Pd, B, In and the like, to a base of 38 to 60 wt % Nixe2x80x94Fe two-element alloy.
The results were found to be a composition range and a fabrication method of an outstanding thin film having a saturation magnetic flux density (BS) larger than 1.5 T, a magnetic coercive force in the hard axis direction (HCH) smaller than 1.0 Oe and a resistivity larger than 40 xcexcxcexa9xc2x7cm, while keeping the film thickness of 2 to 5 xcexcm which is required for the recording magnetic field.
By using this material for a thin film magnetic head, it is possible to provide a high performance disk storage system having areal density of 500 MB/in2, a recording frequency of 45 MHz and a transmission speed of above 15 MB/s.
The present invention is characterized by a disk storage system comprising a thin film magnetic disk for recording information, rotating means for the thin film magnetic disk, a thin film magnetic head for performing writing and reading of information and provided in a floating type slider, transfer means for supporting the floating type slider and for making access to the thin film magnetic disk.
The present invention is characterized by a disk storage system wherein at least one of an upper magnetic core and a lower magnetic core the write head is made of a metallic magnetic material having an average crystal grain size smaller than 500 xc3x85, a resistivity at room temperature larger than 40 xcexcxcexa9xc2x7cm and a magnetic coercive force in the hard axis direction smaller than 1.0 Oe.
The present invention is characterized by the fact that, in a disk storage system, at least one of an upper magnetic core and a lower magnetic core of the writing magnetic core of the write head is an electroplated thin film made of a Nixe2x80x94Fe group alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt %.
Further, the present invention is characterized by a disk storage system comprising a magnetic disk having a transfer rate larger than 15 mega-bytes per second, areal density of recording data larger than 500 mega-bits per square inch and a diameter smaller than 3.5 inches.
The present invention is characterized by a disk storage system wherein the magnetic disk rotates faster than 4000 rpm during recording and reproducing, the recording frequency is larger than 45 MHz, and at least an upper magnetic core of a thin film magnetic head for performing the recording is made of a Nixe2x80x94Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and having a film thickness of 1 to 5 xcexcm, an average crystal grain size smaller than 500 xc3x85, a resistivity of 40 to 60 xcexcxcexa9xc2x7cm and magnetic coercive force in the hard axis direction smaller than 1.0 Oe, the recording magnetomotive force of the write head being larger than 0.5 ampere-turns.
The magnetic core in a disk storage system according to the present invention contains a substance composed of at least one kind of one of Co less than 15 wt % and Mo, Cr, Pd, B, In less than 3 wt % in the total weight.
Further, the present invention is characterized by a disk storage system comprising a thin film magnetic disk for recording information, rotating means for the thin film magnetic disk, a dual element head for performing writing and reading of information with individual elements provided in a floating type slider, and transfer means for supporting the floating type slider and for making access to the thin film magnetic disk.
The present invention is characterized by a disk storage system wherein the magnetic film having the same characteristics and the same composition as those described above are used for the magnetic film of the write head.
Furthermore, the present invention is characterized by a disk storage system comprising a magnetic disk having a transfer rate larger than 15 mega-bytes per second, areal density of recording data larger than 500 mega-bits per square inch and a diameter of a magnetic disk smaller than 3.5 inches.
The present invention is characterized by a disk storage system wherein the magnetic disk rotates faster than 4000 rpm during recording and reproducing, the recording frequency being larger than 45 MHz, a dual element head for performing the recording and the reproducing with individual elements, the film having the same characteristics and the same composition as those described above and being used for at least an upper magnetic core of a write head.
The present invention is characterized by a thin film magnetic head comprising a lower magnetic film, an upper magnetic film formed on the lower magnetic film, one end contacting one end of the lower magnetic film, the other end facing the other end of the lower magnetic film through a magnetic gap, whereby the upper magnetic film forms a magnetic circuit including the magnetic gap together with the lower magnetic film, and a conductive coil forming a coil having a given number of winding turns passing between both of the magnetic films.
The present invention is characterized by a thin film magnetic head wherein at least one of the upper magnetic film and the lower magnetic film is formed through a plating method, being made of a Nixe2x80x94Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and having a film thickness of 1 to 5 xcexcm, an average crystal grain size smaller than 500 xc3x85, and a magnetic coercive force in the hard axis direction smaller than 1.0 Oe.
The present invention involves a fabrication method of a thin film magnetic head comprising a lower magnetic film, an upper magnetic film formed on the lower magnetic film, one end contacting one end of the lower magnetic film, the other end facing the other end of the lower magnetic film through a magnetic gap, whereby the upper magnetic film forms a magnetic circuit including the magnetic gap together with the lower magnetic film, and a conductive coil forming a coil having a given number of winding turns passing between both of the magnetic films.
The present invention involves a fabrication method of a thin film magnetic head wherein at least one of the lower and the upper magnetic films is formed by electroplating using a Nixe2x80x94Fe electroplating bath containing a metallic ion concentration of Ni++ ions of 15 to 20 g/l and Fe++ ions of 2.0 to 2.7 g/l, the ratio of the Ni++ ions and the Fe++ ions (Ni++/Fe++) being 7 to 8, and containing a stress release agent and a surface active agent, the pH being 2.5 and 3.5.
Particularly, it is preferable for the thin film magnetic head to be formed by electroplating though a mask in a magnetic field while keeping the temperature of the plating bath at 20 to 35xc2x0 C. and a current density of 5 to 30 mA/cm2.
Further, in the present invention, it is preferable that the thin film magnetic head comprises a magnetic core, the magnetic film being formed using a plating bath to which is added Co ions of 0.4 to 0.6 g/l and/or Cr, Mo, Pd, In, B less than 0.1 g/l.
Further, it is preferable that the magnetic film of the thin film magnetic head is formed by electroplating though a mask in a magnetic field.
In the present invention, writing blur due to the recording frequency and fluctuation of an over-write value are prevented by designing the thickness, resistivity and relative permeability of a magnetic film of a magnetic pole for a write head while taking eddy current loss into consideration, and at the same time by setting the data recording frequency to a high value and rotating a magnetic disk fitted to the above head at a high speed.
(1) It is preferable to provide a means having a transfer rate higher than 15 mega bytes per second, areal density larger than 500 mega bits per square inch.
(2) It is preferable that when storing of information is performed using a magnetic disk having a diameter smaller than 3.5 inches, the magnetic disk is rotated at 4000 rpm during recording and reproducing, and the recording frequency is set to a value above 45 MHz.
(3) It is preferable to provide a magnetic disk using a metallic film having a magnetic coercive force larger than 2 kOe.
(4) It is preferable to set the build-up time of the recording current to a value smaller than 5 nano-seconds (ns).
(5) It is preferable for the coil of an inductive head for performing recording of information on a magnetic disk to be formed through a thin film process, for the number of terminals to be three, and for the inductance between the terminals to be smaller than 1 micro-henry (xcexcH).
(6) It is preferable for the coil of an inductive head for performing recording of information on a magnetic disk to be of a two-layer structure, for the number of winding turns in the first layer to be equal to that in the second layer, and for the directions of winding to be opposite to each other.
(7) It is preferable for the coil of an inductive head for performing recording of information on a magnetic disk to be of a single-layer structure, and an additional terminal to be connected to a position (c) corresponding to one-half of the number of winding turns between the starting point of the coil (a) and the end point of the coil (b), and for the current flowing between (c) and (a) and the current flowing between (c) and (b) to be in opposite phase to each other.
(8) Letting the film thickness of a magnetic film of a core of an inductive head be d (xcexcm), resistivity be xcfx81 (xcexcxcexa9xc2x7cm) and the relative permeability at a low frequency be xcexc, it is preferable to provide a means in which these parameters satisfy the relation xcexcd2/xcfx81xe2x89xa6500.
(9) It is preferable for at least a part of the recording magnetic pole of a magnetic head used for data recording or data recording and reproducing to be of a multi-layer structure in which a magnetic layer and an insulator layer are alternatively laminated, and for the thickness of the film to be thinner than 2.7 xcexcm.
(10) It is preferable for the Fexe2x80x94Ni alloy described above to be used for at least the upper magnetic film of the recording magnetic films of a magnetic head used for data recording or data recording and reproducing, and for a Co base amorphous alloy or an Fe base amorphous alloy to be used for the lower magnetic film.
(11) It is preferable for the material of the recording magnetic pole contains at least one of Zr, Y, Ti, Hf, Al and Si.
(12) It is preferable for the recording magnetomotive force, that is, the product of recording current and number of winding turns of the coil of a magnetic head used for data recording or data recording and reproducing, to be set to a value larger than 0.5 ampere turns (AT).
(13) It is preferable for the resistivity of at least a part of the recording magnetic pole of a magnetic head used for data recording or data recording and reproducing to be larger than 40 xcexcxcexa9xc2x7cm and for the relative permeability to be larger than 500.
(14) It is preferable for the recording coil of an inductive head for performing recording of information on a magnetic disk medium to be of a single-layer structure, for an additional terminal to be connected to a position (c) corresponding to one-half of the number of winding turns between the starting point of the coil (a) and the end point of the coil (b), for the current flowing between (c) and (a) and the current flowing between (c) and (b) to be in opposite phase to each other, and for a dual element head using a spin valve element and a giant magnetoresistive element to be used as the reproducing head.
In the high frequency band above the recording frequency of 45 MHz, the head efficiency (efficiency to induce magnetic flux) of the magnetic head is dominated by the eddy current loss. Although, in order to decrease the eddy current loss, it is most effective to decrease the film thickness of the magnetic core, decreasing of the film thickness causes a recording incapability due to a shortage in the recording magnetic flux.
In order to sufficiently record on a medium having a high magnetic coercive force larger than 2000 Oe, particularly above 2300 Oe, the film thickness is required to be larger than 2 xcexcm and the saturation magnetic flux density is required to be high. In general, a multi-layer film may be employed for decreasing the eddy current loss, but the head process for coping with the high recording density makes it difficult to obtain a high accuracy in the dimensions.
Therefore, it is necessary to decrease the eddy current loss by increasing the resistivity of the magnetic core in order to extend the frequency characteristic of the permeability (xcexc) of the magnetic core up to a high frequency.
The Nixe2x80x94Fe magnetic film (3 xcexcm film thickness) shows a saturation magnetic flux density (BS) larger than 1.5 T and a resistivity (xcfx81) of 40 to 50 xcexcxcexa9xc2x7cm when the Ni concentration is within the range of 38 to 60 wt %. That is, when the Ni concentration is below 38 wt %, the specific resistivity (xcfx81) is large, but the saturation magnetic flux density (BS) becomes lower than 1.5 T.
On the other hand, when the Ni concentration is above 60 wt %, the saturation magnetic flux density (BS) also becomes lower than 1.5 T. Especially, it is preferable for the concentration of Ni to be 40 to 50 wt %.
A plating process is suitable for fabricating a film having such a composition. That is, since the crystal grain size can be made very small using an electroplating method, the magnetic coercive force can be made small and the orientation of the crystal can be decreased as low as possible even in a case of a composition having a large magnetocrystalline anisotropy. For example, it is preferable that the orientation ratio of the crystal is suppressed below 5.0, that is (111)/(200) less than 5.0.
The composition of a plating bath for fabricating such a film has Ni and Fe ion concentrations at Ni++: 15 to 20 g/l, Fe++: 2.0 to 2.7 g/l, and the ion ratio (Ni++/Fe++) at 7 to 8. In this case, the plating current density is 10 to 20 mA/cm2, the pH is 3.0, and the bath temperature is 30xc2x0 C.
On the other hand, in the case of adding at least one of the elements Co, Mo, Cr, B, In and Pd, it is preferable for the Co to be less than 15 wt % and for the Mo to be less than 3 wt % in order to keep the saturation magnetic flux density (BS) higher than 1.5 T and the resistivity (xcfx81) larger than 40 xcexcxcexa9xc2x7cm.
In a case of using Co as a component in the bath, it is preferable to add up to CoSO4.6H2O of 100 g/l (Co ions of 21 g/l), and in a case of Mo, Na2MoO4.2H2O of 4.8 g/l (Mo ions of 1.9 g/l). For example, in a case of adding Cr [Cr2(SO4)3.18H2O] instead of Mo, the same effect can be observed In a case of adding B or In, the resistivity (xcfx81) is increased not as much as about 10%.
On the other hand, in the case of adding Co, the saturation magnetic flux density (BS) is increased by nearly 10%, though the resistivity (xcfx81) of the film is slightly deceased. Therefore, it is preferable to use Co together with Mo. Further, since Co increases the anisotropic magnetic field (HK), Co is preferable for stabilizing the magnetic characteristic.
When Co is added in an amount more than 15 wt %, the saturation magnetic flux density (BS) of the film is increased, but the resistivity (xcfx81) of the film is deceased too much. Therefore, the resistivity (xcfx81) of the film cannot be increased up to a desired value unless a large amount of Mo, Cr are added.
This is not preferable because the magnetic coercive force of the film becomes large. In order to increase the resistivity (xcfx81) without increasing the magnetic coercive force of the film, the amount of Mo, Cr to be added should be limited to 3 wt % or less.
In the case of adding B, In, Pd or the like, the amount added should be limited as indicated above. In these cases, the plating condition may be the same as in the case of a Nixe2x80x94Fe magnetic film, as described above.
Assuming that the high frequency loss (tan xcex4) of the magnetic film is attributed only to the eddy current loss, the high frequency loss can be expressed by the following equation:                                                                         tan                ⁢                                  xe2x80x83                                ⁢                δ                            =                                                μ                  xe2x80x3                                /                                  μ                  xe2x80x2                                                                                                        =                                                R                  /                  ω                                ⁢                                  xe2x80x83                                ⁢                L                                                                                        =                                                μ                  0                                ⁢                μ                ⁢                                  xe2x80x83                                ⁢                                  ∏                                                            d                      2                                        ⁢                                          f                      /                      C                                        ⁢                                          xe2x80x83                                        ⁢                    ρ                                                                                                          (        1        )            
where xcexcxe2x80x2 and xcexcxe2x80x3 are a real part and an imaginary part of the complex magnetic permeability. C is a constant determined by the shape of the film, and xcexc0 is the permeability of a vacuum.
From the above equation (1), when the relative permeability xcexc inherent in the magnetic film, the film thickness d, and the resistivity xcfx81 are given, the eddy current loss tan xcex4 corresponding to the frequency f can be obtained. Since the change of the head efficiency (efficiency to induce magnetic flux) corresponding to the frequency is proportional to the change in the real part of the complex permeability, the frequency dependence of the head efficiency can be obtained by calculating xcex4 from Equation (1) and taking the cosine component.
That is, the head efficiency xcex7 for each frequency can be expressed by the following equation.
xcex7=cos[arctan(xcexc0xcexcΠd2f/Cxcfx81)]xe2x80x83xe2x80x83(2)
From Equation (2), by specifying the value xcexcd2/xcfx81 which can be obtained from the relative permeability xcexc inherent in the magnetic film, the film thickness d and resistivity xcfx81, the head efficiency xcex7 for an arbitrary frequency f can be extrapolated.
By combining the above head and a magnetic disk using a metallic magnetic film having a magnetic coercive force larger than 2 kOe, which exhibits a small write blurring during high frequency recording and a small fluctuation of overwriting, it is possible to obtain a high performance disk storage system having areal density larger than 500 MB/in2, a recording frequency higher than 45 MHz and a transfer rate higher than 15 MB/s.
In a case of using a fast and wide SCSI (Small Computer System Interface) having a data bus of two-byte width as an I/O interface, from the relationship between the price of an input/output device and a transfer rate per one magnetic disk device composing the input/output device, it is possible to transmit data up to 20 MB/s at a maximum when the fast and wide SCSI having a data bus of two-byte width as an I/O interface is used.
In this case, when the transfer rate per one magnetic disk device is above 15 MB/s, it can be understood that the price of the input/output device can be decreased.
Further, when the capacity per one magnetic disk device is 550 MB, it is possible to employ an OS (Operation Software) such as Windows, Workplace and the like. In order to realize this capacity with one magnetic disk of 3.5 inch type, areal density capable of recording the data is required to be 500 MB/in2.
According to the present invention, a recording head, which is capable of performing sufficient recording to a medium having a high magnetic coercive force and at a high frequency range, is fabricated by a specified composition and through a low cost electroplating method.
Thereby, it is possible to obtain a disk storage system with a high recording density capable of a high data transfer rate, decreasing access time and increasing memory capacity by keeping a transfer rate higher than 15 MB/s, a recording frequency higher than 45 MHz, and the rotating speed of the magnetic disk higher than 4000 rpm.